I. Field of the Invention
The present invention relates generally to a soft, flexible material. More particularly, it relates to a thermoplastic composition that can be used to make a variety of products that are soft and flexible. The thermoplastic composition is, preferably, a combination of a polyolefin and thermoplastic elastomeric materials. In addition, the thermoplastic composition may include one or more additional thermoplastic materials. Some uses envisioned for this composition are, for example, catamenial devices, baby care products, such as baby bottles and holders, pacifiers, toothbrushes and containers. One particular use of the composition is for a tampon applicator and especially a tampon applicator barrel, that will be more comfortable and has a greater ease of insertion into the vagina greater ease of insertion into the vagina than known such applicator barrels.
II. Description of the Prior Art
Polyethylene is a thermoplastic that is the standard resin used to produce a number of products, including plastic tampon applicators. A softer applicator, especially an applicator barrel, that is more comfortable is a desirable feature of a tampon applicator in order to provide improved ease of insertion.
It is generally known that thermoplastic elastomer articles may be combined with polyethylene to improve the strength and toughness of such articles. For example, U.S. Pat. No. 4,593,063 to M. A. Jones, et al., which issued Jun. 3, 1986, provides a reinforced rigid polymer blend which yields a high gloss finish when injection molded. The thermoplastic elastomer includes 25 to 35 percent of a butadiene thermoplastic elastomer having a molecular weight of about 70,000 to about 100,000, a styrene content from about 25 to about 44 percent by weight and a melt flow rate from about 8 to about 15 grams per 10 minutes. The butadiene thermoplastic elastomer is blended with from about 54 to about 75 percent of a rigid polymer, such as polyethylene.
Polymers have also been combined with polyethylene to improve their reaction to each other when heated or otherwise processed. For example, U.S. Pat. No. 4,678,834 to D. W. Boivin, et al., which issued Jul. 7, 1987, provides a polyolefin blend comprising a major portion of polyethylene and a minor portion of a second polymer, such as a styrene-butadiene-styrene copolymer. The second polymer contains a reactive agent that is capable of reacting with polyolefins in a molten state. The reactive agent modifies or stabilizes the polymer during processing or during use.
Polymers may also be added to polyethylene to permit a breakdown of its structural composition. Polyethylene, which is normally stable, has also been combined with less stable materials to produce biodegradable products. Such biodegradable products include ingredients that cause oxidative actions in order to break down the polyethylene. For example, U.S. Pat. No. 5,212,219 to G. J. L. Griffin, which issued May 18, 1993, provides a degradable article prepared from a blend of polyethylene and a less stable polymer or copolymer, such as a styrene-butadiene block copolymer. The composition further comprises an antioxidant active over a limited period and a pro-oxidant that causes a sharp loss of physical strength on depletion of the anti-oxidant. In addition, the presence of filler particles of a biologically sensitive material accelerates the biological breakdown of the polymer/copolymer blend.
Improvements to the pelletizability and drapability of a polymer composition, without causing the composition to biodegrade, are also known. For example, U.S. Pat. No. 4,833,195 to A. M. Adur, et al., which issued May 23, 1989, provides a thermoplastic polymer composition that can be conveniently converted into a drapable film or fabric. The composition has a low Shore A hardness, i.e., below about 95, and a high melt flow rate about 30 grams/10 minutes to 1100 grams/10 minutes at 230 degrees Celsius and 2.16 kilograms. Drapability is an important property of products that drape against a user""s skin, such as baby diapers or sanitary napkins.
However, none of the above patents describe or suggest a tampon applicator that is composed of such materials. In fact, none of the above patents suggest the inventive combination of polyethylene and the unique elastomeric composition which improves flexibility, strength and tear resistance and, perhaps, softness, and can function as a compatibilizer with other thermoplastic polymeric materials. Thus, the above patents do not suggest a flexible, soft tampon applicator having a unique blend of polyethylene and a rubber type composition that includes a thermoplastic elastomer (TPE), namely a styrene-butadiene-styrene block copolymer, which applicator provides for comfortable and easy insertion into the vagina.
Further, thermoplastic resins are much less expensive than elastomeric materials. To minimize the costs of tampon applicators, one desires the greatest amount of thermoplastic resin as possible in the composition, but without adverse affects. Accordingly, to achieve the benefits of a flexible and easy to insert tampon applicator barrel and yet minimize costs, it is desired to use as little as possible of the elastomer components and as much as possible of the thermoplastic resin component in the tampon applicator barrel.
Other projected products, such as, for example, a holder for nurser liners or a nurser bottle, may desire the flexibility of the material in order to assist a child or parent in gripping the product and, perhaps, squeeze the product to remove contents.
Against the for going background, it is a primary object of the present invention to provide a composition that comprises a polyolefin and a thermoplastic elastomer.
It is another object of the present invention to provide such a composition that favorably adjusts the modulus of elasticity of the composition.
It is yet another object of the present invention to provide such a composition in a thermoplastic-type tampon applicator so that the barrel, in particular, is soft and flexible to provide more comfort and improved ease of insertion.
It is a further object of the present invention to provide such a tampon applicator at least one styrene-butadiene-styrene block copolymer to achieve such desired properties.
To accomplish the foregoing objects and advantages, the present invention, in brief summary, is a soft, flexible composition that comprises a thermoplastic resin and at least two styrene-butadiene-styrene block copolymers, each having a different percent by weight of styrene in an amount sufficient to reduce the modulus of elasticity.
A preferred use of the composition is as a tampon applicator barrel that is more comfortable and has improved ease of insertion into the vagina. The tampon applicator barrel comprises a thermoplastic resin and at least one thermoplastic elastomer in an amount sufficient to adjust favorably the modulus of elasticity of the tampon applicator barrel.
More specifically, the present invention is a soft, flexible tampon applicator that provides more comfort and improved ease of insertion into the vagina by the combination of a low density polyethylene and at least one styrene-butadiene-styrene block copolymer. In one preferred embodiment, there are at least two styrene-butadiene-styrene block copolymers, each having a different percent by weight of styrene.
In a most preferred embodiment, there are three styrene-butadiene-styrene block copolymers each having a percentage by weight of styrene that is different than that of the other two copolymers. In particular, the first styrene-butadiene-styrene block copolymer has about 29 percent by weight of styrene, the second styrene-butadiene-styrene block copolymer has about 31 percent by weight of styrene, and the third styrene-butadiene-styrene block copolymer has about 43 percent by weight of styrene.
The polymeric resin should further comprise one or more of the following: a plasticizer and a compatibilizer/flow modifier, and may further comprise other ingredients, such as a pigment, a slip/mold release agent, an antioxidant and, perhaps, an antistat ingredient.
The present invention is also a method for making a composition that can be made into a soft, flexible product. An elastomer composition is melted and combined to form a melted resin which is then extruded into a plurality of soft resin pellets. The plurality of soft resin pellets are then dry blended with a plurality of pellets of a polyolefin, for example, low density polyethylene to form a pellet mixture. Finally, the pellet mixture is melted together to form a polymeric compound that may be molded to a desired shape. In a preferred embodiment, the method is used to make a tampon applicator, especially an applicator barrel, that has a soft and flexible structure for more comfort and improved ease of insertion into the vagina.